Vehicle occupant detection systems are useful in connection with air bags and other pyrotechnically deployed restraints as a means of judging whether, and how forcefully, to deploy the restraint. One fundamental parameter in this regard is the weight of the occupant, as weight may be used as a criterion to distinguish between an adult and an infant or small child.
Most prior weight estimation techniques involve installing a pressure sensitive element such as a variable resistance pad or a fluid filled bladder in or under a vehicle seat cushion, and utilizing the pressure measurement as an indication of occupant weight. See, for example, the U.S. Pat. Nos. 5,474,327, 5,987,370, 6,246,936, 6,101,436 and 6,490,936, assigned to the assignee of the present invention and incorporated by reference herein.
Alternatively, the occupant weight may be measured with one or more load cells that sense the forces (strain or pressure) that the seat applies to a bracket that supports the seat on the vehicle floor. See, for example, the Publication Nos. 41520, 41542, 41549 and 41559 from the November, 1998 issue of Research Disclosure. However, frame-based weight estimation is subject to significant error in cases where a foreign object such as a beverage container is placed on the floor under the seat and the undercarriage of the seat comes into contact with the object when occupant weight causes downward deflection of the seat cushion and springs. In such cases, a significant portion of the occupant weight can be shunted to the floor through the object instead of the seat frame and floor brackets, and the frame-based force measurement will indicate an erroneously low occupant weight. Accordingly, what is needed is a frame-based occupant weight estimation apparatus that is not subject to error due to partial load shunting through foreign objects placed under the seat.